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A.I. gratefully acknowledges the financial support of The Faculty of Science and Technology at Aarhus University through a Sabbatical scholarship and the hospitality of the Quantum Technology group, the Centre for Theoretical Atomic, Molecular and Optical Physics and the School of Mathematics and Physics, during his stay at Queen’s University Belfast. A.B. acknowledges the hospitality of the Institute for Theoretical Physics and the “Nonequilibrium quantum dynamics” group at Universität Stuttgart, where part of this work was carried out. R.P. and M.P. acknowledge the support by the SFI-DfE Investigator Programme (Grant No. 15/IA/2864) the Eropean Union’s Horizon 2020 FET-Open project SuperQuLAN (899354) and TEQ (766900). M.P. acknowledges support by the Leverhulme Trust Research Project Grant UltraQuTe (Grant No. RGP-2018-266), the Royal Society Wolfson Fellowship (RSWF/R3/183013), the UK EPSRC (Grant No. EP/T028424/1) and the Department for the Economy Northern Ireland under the US-Ireland R&D Partnership Programme. A.B. also acknowledges support from H2020 through the MSCA IF pERFEcTO (Grant Agreement No. nr. 795782) and from the DeutscheForschungsgemeinschaft (DFG, German Research Foundation) Project No. BR5221/4-1. We consider a finite one-dimensional chain of quantum rotors interacting with a set of thermal baths at different temperatures. When the interaction between the rotors is made chiral, such a system behaves as an autonomous thermal motor, converting heat currents into non-vanishing rotational ones. Such a dynamical response is strongly pronounced in the range of the Hamiltonian parameters for which the ground state of the system in the thermodynamic limit exhibits a quantum phase transition. Such working points are associated with large quantum coherence and multipartite quantum correlations within the state of the system. This suggests that the optimal operating regime of such quantum autonomous motor is one of maximal quantumness. 9 pages, 9 figures Peer reviewed

Quantizing large Neural Networks (NN) while maintaining the performance is highly desirable for resource-limited devices due to reduced memory and time complexity. It is usually formulated as a constrained optimization problem and optimized via a modified version of gradient descent. In this work, by interpreting the continuous parameters (unconstrained) as the dual of the quantized ones, we introduce a Mirror Descent (MD) framework for NN quantization. Specifically, we provide conditions on the projections (i.e., mapping from continuous to quantized ones) which would enable us to derive valid mirror maps and in turn the respective MD updates. Furthermore, we present a numerically stable implementation of MD that requires storing an additional set of auxiliary variables (unconstrained), and show that it is strikingly analogous to the Straight Through Estimator (STE) based method which is typically viewed as a "trick" to avoid vanishing gradients issue. Our experiments on CIFAR-10/100, TinyImageNet, and ImageNet classification datasets with VGG-16, ResNet-18, and MobileNetV2 architectures show that our MD variants obtain quantized networks with state-of-the-art performance. Code is available at https://github.com/kartikgupta-at-anu/md-bnn. Comment: This paper was accepted at AISTATS 2021

We report measurements of energy-dependent attosecond photoionization delays between the two outer-most valence shells of N$_2$O and H$_2$O. The combination of single-shot signal referencing with the use of different metal foils to filter the attosecond pulse train enables us to extract delays from congested spectra. Remarkably large delays up to 160 as are observed in N$_2$O, whereas the delays in H$_2$O are all smaller than 50 as in the photon-energy range of 20-40 eV. These results are interpreted by developing a theory of molecular photoionization delays. The long delays measured in N$_2$O are shown to reflect the population of molecular shape resonances that trap the photoelectron for a duration of up to $\sim$110 as. The unstructured continua of H$_2$O result in much smaller delays at the same photon energies. Our experimental and theoretical methods make the study of molecular attosecond photoionization dynamics accessible. 5 pages, 3 figures, accepted in Phys. Rev. Lett

In the future of Ancillary Services for the HV grid, Demand Side Response (DSR) will play an increasingly important role to ensure grid stability and promote Renewable Energy Sources integration in the electrical system. A particular use case of the Italian Demo of the H2020 project “Optimal System-Mix Of flexibility Solutions for European electricity” (OSMOSE) is to demonstrate multiple grid services provision based on DSR by seven industrial plants distributed in a HV grid area between Apulia and Basilicata. Sites have been managed by three Balance Service Providers (BSPs). On each industrial plant, project partners first have performed an energy audit and then they have installed all the electric and TLC equipment needed to test and manage the flexibilities identified. The main result of these activities was that the hardware required for DSR comes at a relatively small price compared to the magnitude of loads that could be controlled. Purpose of this work is to provide an analysis of possible benefits and limits of DSR for the grid as well as to direct a possible new future market strategy for these resources.

Abstract Discrete time-translational symmetry in a periodically driven many-body system can be spontaneously broken to form a discrete time crystal, an exotic new phase of matter. We present observations characteristic of discrete time crystalline order in a driven system of paramagnetic P-donor impurities in isotopically enriched 28Si cooled below 10 K. The observations exhibit a stable subharmonic peak at half the drive frequency which remains pinned even in the presence of pulse error, a signature of discrete time crystalline order. This signal has a finite lifetime of ∼100 Floquet periods, but this effect is long-lived relative to coherent spin–spin interaction timescales, lasting ∼104 times longer. We present simulations of the system based on the paradigmatic central spin model and show good agreement with experiment. We investigate the role of dissipation and interactions within this model, and show that both are capable of giving rise to discrete time crystal-like behaviour.

Tetrahedrally-bonded materials, such as silicon, diamond, or gallium nitride, are characterized by a low coordination number of 4 in the crystalline phase and, in general, can exhibit a liquid phase with higher density and coordination. This leads to interesting thermodynamic behavior, including the lowering of the melting temperature with increasing pressure and the possible existence of distinct low- and high-density liquid phases. Using molecular dynamics simulations, we explored the role of pressure and the degree of tetrahedrality on the structure and phase equilibria between the crystalline and liquid phases of tetrahedrally-bonded materials. In addition to the thermodynamic melting point, we determined the temperature of mechanical stability (spinodal temperature) as a function of pressure. The latter temperature is relevant to the laser pulse rapid melting of tetrahedrally-bonded materials. The results of our simulations indicate the possibility of the existence of a thermodynamically stable low-density liquid phase of silicon at high pressures. Our simulation also suggests that GaN is unlikely to exhibit anomalous thermodynamic behavior due to a high degree of tetragonality preventing the formation of high-density liquid, even at high pressures.Tetrahedrally-bonded materials, such as silicon, diamond, or gallium nitride, are characterized by a low coordination number of 4 in the crystalline phase and, in general, can exhibit a liquid phase with higher density and coordination. This leads to interesting thermodynamic behavior, including the lowering of the melting temperature with increasing pressure and the possible existence of distinct low- and high-density liquid phases. Using molecular dynamics simulations, we explored the role of pressure and the degree of tetrahedrality on the structure and phase equilibria between the crystalline and liquid phases of tetrahedrally-bonded materials. In addition to the thermodynamic melting point, we determined the temperature of mechanical stability (spinodal temperature) as a function of pressure. The latter temperature is relevant to the laser pulse rapid melting of tetrahedrally-bonded materials. The results of our simulations indicate the possibility of the existence of a thermodynamically stable low-d...

A lot has changed since that day on December 17, 1903 when the Wright brothers made the first powered manned flight. Even though the concepts behind flying are unaltered, appearance of stat-of-the-art modern aircrafts has undergone a massive evolution. This is mainly owed to our deeper understanding of how to harness and optimize the interaction between fluid flows and aircraft bodies. Flow passing over wings and different junctions on an aircraft faces numerous local features, for instance, acceleration or deceleration, laminar or turbulent state, and interacting boundary layers. In our study we aim to characterize some of these flow features and their physical roles. Primarily, stability characteristics of flow over a wing subject to a negative pressure gradient are studied. This is a common condition for flows over swept wings. Part of the current numerical study conforms to existing experimental studies where a passive control mechanism has been tested to delay laminarturbulent transition. The same flow type has also been considered to study the receptivity of three-dimensional boundary layers to freestream turbulence. The work entails investigation of effects of low-level freestream turbulence on crossflow instability, as well as interaction with micron-sized surface roughness elements. Another common three-dimensional flow feature arises as a resultof stream-lines passing through a junction, the so-calledcorner-flow. For instance, thisflow can be formed in the junction between the wing and fuselage on aplane.A series of direct numerical simulations using linear Navier-Stokes equationshave been performed to determine the optimal initial perturbation. Optimalrefers to perturbations which can gain the maximum energy from the flow overa period of time. In other words this method seeks to determine theworst-casescenario in terms of perturbation growth. Here, power-iterationtechnique hasbeen applied to the Navier-Stokes equations and their adjoint to determine theoptimal initial perturbation. Recent advances in super-computers have enabled advance computational methods to increasingly contribute to design of aircrafts, in particular for turbulent flows with regions of separation. In this work we investigate theturbulentflow on an infinite wing at a moderate chord Reynolds number of Re= 400,000 using a well resolved direct numerical simulation. A conventional NACA4412 has been chosen for this work. The turbulent flow is characterizedusing statistical analysis and following time history data in regions with interesting flow features. In the later part of this work, direct numerical simulation has been chosen as a tool to mainly investigate the effect of freestream turbulence on the transition mechanism of flow from laminar to turbulent around a turbine blade. QC 20151125

Abstract Background Beer is the most popular alcoholic beverage worldwide. In the manufacture of beer, various by-products and residues are generated, and the most abundant (85% of total by-products) are spent grains. Thanks to its high (hemi)cellulose content (about 50% w/w dry weight), this secondary raw material is attractive for the production of second-generation biofuels as butanol through fermentation processes. Results This study reports the ability of two laccase preparations from Pleurotus ostreatus to delignify and detoxify milled brewer’s spent grains (BSG). Up to 94% of phenols reduction was achieved. Moreover, thanks to the mild conditions of enzymatic pretreatment, the formation of other inhibitory compounds was avoided allowing to apply the sequential enzymatic pretreatment and hydrolysis process (no filtration and washing steps between the two phases). As expected, the high detoxification and delignification yields achieved by laccase pretreatment resulted in great saccharification. As a fact, no loss of carbohydrates was observed thanks to the novel sequential strategy, and thus the totality of polysaccharides was hydrolysed into fermentable sugars. The enzymatic hydrolysate was fermented to acetone-butanol-ethanol (ABE) by Clostridium acetobutilycum obtaining about 12.6 g/L ABE and 7.83 g/L butanol within 190 h. Conclusions The applied sequential pretreatment and hydrolysis process resulted to be very effective for the milled BSG, allowing reduction of inhibitory compounds and lignin content with a consequent efficient saccharification. C. acetobutilycum was able to ferment the BSG hydrolysate with ABE yields similar to those obtained by using synthetic media. The proposed strategy reduces the amount of wastewater and the cost of the overall process. Based on the reported results, the potential production of butanol from the fermentation of BSG hydrolysate can be envisaged.

abstract

Abstract Trust problems are ubiquitous in social and economic exchange. They are known to be mitigated if exchange partners are embedded in social structures that disseminate information on past behavior. If such “network embeddedness” makes exchanges possible that would not be possible otherwise, it is also expected that actors are willing to exert effort to establish embeddedness. Theory suggests that the degree to which network embeddedness facilitates trust depends on the size of the trust problem, and there are reasons to expect that embeddedness facilitates trust more strongly if it is established endogenously rather than imposed exogenously. We tested these predictions in a laboratory experiment in which 342 participants played repeated trust games with exogenous or endogenous embeddedness under varying sizes of the trust problem. The results confirm that embeddedness promotes trustfulness and trustworthiness. The results also show that endogenously chosen embeddedness promotes trustfulness more strongly than exogenously imposed embeddedness. However, we find no systematic variation in investments in embeddedness or effects of embeddedness in the size of the trust problem.